Concrete form duct chair and method

ABSTRACT

An improved concrete form duct chair and method of forming concrete structures. The concrete form duct chair has a generally flat polymer or steel body with several pre-stressing strand duct sized apertures passing through the body, as well as four or more alignment legs projecting from the body, the alignment legs and body dimensioned and configured to extend for a total width approximately equal to such cross sectional width of such concrete form and thus hold the concrete form duct chair in position against the walls of the form. Concrete access apertures passing through the body allow concrete to pass therethrough during pouring operations. A method embodiment of the invention teaches pouring of concrete structures with pre-stressing ducts passing therethrough using the device of the invention to retain the pre-stressing ducts in alignment within the concrete form.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 37 CFR 1.71(d).

CROSS-REFERENCE TO RELATED APPLICATIONS

N/A

FIELD OF THE INVENTION

This invention relates generally to concrete form devices, and specifically to duct chair devices for preformed or prestressed concrete structures.

STATEMENT REGARDING FEDERALLY FUNDED RESEARCH

This invention was not made under contract with an agency of the US Government, nor by any agency of the US Government.

BACKGROUND OF THE INVENTION

Casting of concrete structures, particularly pre-stressed concrete structures, presently allows for creation of a wide variety of extremely strong, and even extremely large, structures falling into a wide range of types. Bridges, buildings, aprons, and other structures may be constructed by pre-casting of large concrete support sections and transporting such sections to the location of construction. In addition to pre-casting, a large number of items are still cast in situ, and the cumulative total of cast concrete items, pre-cast, cast on site, pre-stressed or otherwise, is enormous. U-beams, box beams, I beams, bulb-P beams, aprons, walls, beams, pillars, foundations and anything else cast in place or pre-cast may be considered to have the characteristics and problems discussed herein, although bridge beam sections will be selected as the exemplary context of the present invention.

The paramount consideration in any type concrete casting is the question of safety, which normally devolves to a question of initial strength and maintenance of strength despite aging, weathering and so on.

Normally, a cast bridge section, whether pre-cast at a plant or cast on site, will be a pre-stressed beam section of a tub or box-like cross section. The actual thickness of the pre-cast concrete (and the cross sectional thickness of the form producing it) are actually normally quite thin, that is, the concrete is a (relatively) thin shell surrounding a fairly large interior space.

It is of great importance to the initial and continuing strength of the concrete section that the pre-stressing cable buried in the device are properly positioned at the time of pre-stressing. However, in actual practice, according to the “PCI BRIDGE DESIGN MANUAL”, Chapter Three, FABRICATION AND CONSTRUCTION, section 3.2.1, (page 11 of chapter three), “Plant-cast concrete bridge products are structurally efficient sections which are relatively thin and congested with reinforcements and embedments.”. One immediate concern which arises in that context is the placement of the pre-stressing duct and cable buried in the concrete structure's wall's prior to the pouring of the concrete. The concrete is extremely heavy, of course. As the concrete enters the form, it may move items within the form: reinforcement members (“re-bar” or layers of steel or entire mats of reinforcement members), ducts designed to hold the pre-stressing cables and thus the pre-stressing cables themselves, ducts or other conduits for such items as liquid or electrical cables and so on.

In the event that pre-stressing duct and cable is shifted, the result can be a greatly weakened bridge section, which in turn can conceivably have disastrous consequences. While pre-cast concrete bridges are extremely safe, the real world is not, and it is well documented that ships do frequently ram bridge abutments, trains derail onto bridges, users overload bridges, battle damage brings down bridges and so on. More insidiously, a mis-placed pre-stressed duct and cable may lead to long term issues with the bridge.

Testing by means of ultrasound and drill coring carried out by one company under real-world conditions revealed that pre-stress cable ducts moved during construction or pouring, even though the ducts were properly wired in accordance with industry standard techniques. This resulted in concrete walls that were too thin in places. As miscasting a single bridge section can result in losses of hundreds of thousands or millions of dollars to the company doing the construction, this is both a safety issue and an economic issue, and yet further a compliance issue.

Searching in the United States Patent and Trademark Office collection of patent documents reveals little that is similar to the invention taught herein.

“Bar chairs” or “slab bolsters” are known for holding re-bar in place during casting of concrete products. Such devices are typically elongated polymer or steel articles with numerous pairs of parallel legs for support, the legs typically extending sideways from the body but then making matching ninety degree turns to run the same direction (“down”) and support the device. Such devices resemble nothing so much as a large polymer centipede. (See PRIOR ART FIG. 12). Other types of devices may resemble small polymer stools or the like. (See PRIOR ART FIG. 13). None are known which have the structure of the present invention and thus none are known which resemble the invention.

U.S. Pat. No. 4,021,979 issued to Rez on May 10, 1977, teaches a bracket shaped device for in-lace casting having no structural resemblance to the present invention.

U.S. Pat. No. 4,251,047 to Holtvogt on Feb. 17, 1981 teaches a hold down device having a swivel and multiple bolts, for holding cables, not cable ducts, and entirely lacking legs of any description.

U.S. Pat. No. 4,807,843 issued Feb. 28, 1989 to Courtois et al teaches a plug type device having no apertures or legs.

U.S. Pat. No. 5,259,586 to Miller, Sr. on Nov. 9, 1993 teaches an elaborate offset box beam structure for retention of concrete rather than ducts.

U.S. Pat. No. 5,469,677 issued in the name Luthi on Nov. 28, 1995 teaches an anchor for stressing of concrete, however, the anchor lacks arms, duct apertures and so on.

U.S. Pat. No. 6,047,515 issued to inventor Behlen on Apr. 11, 2000, teaches another type of bracket lacking the structures of the present application: a flat body, apertures, legs and so on.

U.S. Pat. No. 6,155,810 issued to Thim on Dec. 5, 2000 teaches an actual bed or mold for casting of prestressed concrete but does not teach anything relevant to maintaining duct in place.

U.S. Pat. No. 6,550,834 issued to Fromelius on Apr. 22, 2003 teaches an insert designed to create a void space, and lacking arms, a flat body, duct apertures and so on.

U.S. Pat. No. 7,089,710 issued to Nicholson on Aug. 15, 2006 teaches a clamp, having two arms dimensioned and configured to engage a conduit, however, it lacks arms spanning the width of a concrete form, having no flat planar body, and lacking concrete apertures allowing concrete to pass through the body of the device.

U.S. Pat. No. 7,143,991 issued to Hirokawa et al on Dec. 5, 2006 teaches a vaguely cylindrical device which also lacks the features of the present invention.

None of these devices show a substantially planar body with legs projecting in opposite directions to a width equivalent to a form interior width, nor yet duct apertures.

It would be preferable to provide a device and method allowing duct work, particularly pre-stress cable duct work, to be accurately and firmly secured within a concrete form.

It would further be preferable, and is a device, embodiment, aspect, objective and advantage of the present invention to provide a device allowing free flow of concrete through the form.

It would yet further be preferable and is a device, embodiment, aspect, objective and advantage of the present invention to provide a device and method which save on labor of wiring ducts to interior components of a concrete cast and yet is inexpensive to produce and use.

SUMMARY OF THE INVENTION General Summary

The present invention teaches both an improved concrete form duct chair and also an improved method of forming concrete structures. The duct chair of the invention may be used to hold in proper placement pre-stress strand (cable) ducts within a form as concrete is added to the form during the construction of the concrete member.

The concrete form duct chair of the invention has a generally flat body of polymer, metal, wood, etc, the body having passing through itself several apertures dimensioned and configured to accept pre-stressing strand duct, so that the concrete form duct chair may allow the cable ducts to pass through, thereby holding them in place.

Several alignment legs project from the body, either in plane or in other dimensions. The alignment legs and body are dimensioned and configured to extend for a total width approximately equal to such cross sectional width of such concrete form and thus hold the concrete form duct chair in position against the walls of the form. Four or more legs are preferable to provide complete stability.

Concrete access apertures passing through the body allow concrete to pass therethrough during pouring operations, thus helping to avoid void areas within the final concrete structure.

A method embodiment of the invention teaches pouring of concrete structures with pre-stressing strands passing therethrough using the device of the invention to retain the pre-stressing strands in alignment within the concrete form. Several different ordering of the steps of the method of the invention may be used within the scope of the present invention.

Summary in Reference to Claims

It is therefore another aspect, advantage, objective and embodiment of the invention, in addition to those discussed previously, to provide a concrete form duct chair of a concrete form having both a first cross sectional width and a first pre-stressing strand duct, the first pre-stressing strand duct having a first pre-stressing strand duct diameter, the concrete form duct chair comprising:

-   -   a generally flat body;     -   a first duct aperture passing through the body, the aperture         having a first duct aperture diameter approximately equal to         such first pre-stressing strand duct diameter;     -   first and second alignment legs projecting from the body, the         alignment legs and body dimensioned and configured to extend for         a total width approximately equal to such cross sectional width         of such concrete form; and     -   a first concrete access aperture passing through the body, the         concrete access aperture dimensioned and configured to allow         semi-liquid concrete to pass therethrough.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a concrete form duct chair, wherein the material of duct chair comprises one member selected from the group consisting of: polymer, metal, wood, and composites thereof.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a concrete form duct chair, further comprising:

-   -   third and fourth alignment legs projecting from the body, the         third and fourth alignment legs and body dimensioned and         configured to extend for a total width approximately equal to         such cross sectional width of such concrete form.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a concrete form duct chair, further comprising:

-   -   a second duct aperture passing through the body, the aperture         having a second duct aperture diameter approximately equal to         such first pre-stressing strand duct diameter.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a concrete form duct chair, further comprising:

-   -   a second concrete access aperture passing through the body, the         second concrete access aperture dimensioned and configured to         allow semi-liquid concrete to pass therethrough.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a method of casting concrete structures comprising the steps of:

-   -   a) erecting a first concrete form side having an internal cross         sectional width to make a concrete form;     -   b) providing at least one duct chair having a generally flat         body and a first duct aperture passing through the body, the         aperture having a first duct aperture diameter approximately         equal to such first pre-stressing strand duct diameter, the         generally flat body further having at least first and second         alignment legs projecting from the body, the alignment legs and         body dimensioned and configured to extend for a total width         approximately equal to such cross sectional width of such         concrete form, the body further having a first concrete access         aperture passing through the body, the concrete access aperture         dimensioned and configured to allow semi-liquid concrete to pass         therethrough;     -   c) securing the at least one duct chair and a duct passing         through the duct aperture into the concrete form; and     -   d) casting concrete into the concrete form.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a method of casting concrete structures, further comprising:

-   -   e) placing a first mat of reinforcing steel members into the         concrete form prior to securing the duct chair and duct into the         concrete form.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a method of casting concrete structures, further comprising:

-   -   f) placing the duct through the duct chair aperture prior to         securing the duct chair and duct into the concrete form.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a method of casting concrete structures, further comprising:

-   -   g) placing the duct through the duct chair aperture after         securing the duct chair into the concrete form.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a method of casting concrete structures, further comprising:

-   -   h) securing the duct chair in place using fasteners.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a method of casting concrete structures, wherein the fasteners further comprise one member selected from the group consisting of:

-   -   wires, flexible fasteners of plastic/polymer, string, twine,         rope, cable, screws, nails, brads, tacks, bolts, snap fasteners,         hook-and-loop fabric, sleeves, and combinations thereof.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a method of casting concrete structures, further comprising:

-   -   i) placing a second mat of reinforcing steel members into the         concrete form after securing the duct chair and duct into the         concrete form.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a method of casting concrete structures, further comprising:

-   -   j) erecting a second concrete form side defining the internal         cross sectional width between the interior and exterior concrete         form sides.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a method of casting concrete structures, further comprising:

-   -   k) providing a first layer of steel plating in the form.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a method of casting concrete structures, further comprising:

-   -   l) allowing the concrete to cure after pouring.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a method of casting concrete structures, further comprising:

-   -   m) stressing the concrete casting after pouring.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a method of casting concrete structures, further comprising:

-   -   n) stressing the concrete casting immediately after pouring.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a method of casting concrete structures, further comprising:

-   -   o) stressing the concrete casting at a first time duration after         pouring.

It is therefore another aspect, advantage, objective and embodiment of the invention to provide a method of casting concrete structures, further comprising:

-   -   p) separating the concrete casting from the form.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a planform diagram of a first embodiment of the device having four conduit apertures and shorter alignment legs. The diagram may be either a top or bottom view of the device.

FIG. 2 is a planform diagram of a second embodiment of the device having four conduit apertures and longer alignment legs. The diagram may be either a top or bottom view of the device.

FIG. 3 is a planform diagram of a third embodiment of the device having three conduit apertures and shorter alignment legs. The diagram may be either a top or bottom view of the device.

FIG. 4 is a planform diagram of a fourth embodiment of the device having three conduit apertures and longer alignment legs on one side. The diagram may be either a top or bottom view of the device.

FIG. 5 is a side view of an alternative embodiment of the device having three alignment legs per side.

FIG. 6 is a side view of an alternative embodiment of the device having three alignment legs per side.

FIG. 7 is an end view of the device.

FIG. 8 is a cross sectional view of an embodiment of the device in use while a concrete section form is being prepared.

FIG. 9 is a greatly simplified cross sectional view of a prior art U-tub beam with an imposed load.

FIG. 10 is a partial cross-sectional side view of a simple bridge structure showing a single “pre-stressing strand” cable in use in a support beam.

FIG. 11 is a flow chart showing an exemplary method of the invention.

FIG. 12 is a diagram of a PRIOR ART bar chair for holding rebar in place during concrete pouring operations. It may be seen to be completely unsuited by structure to holding ductwork in place.

FIG. 13 is a diagram of a PRIOR ART bar chair of a different type.

INDEX OF REFERENCE NUMERALS

-   Duct aperture 12 -   Concrete aperture 14 -   Leg 16 -   Body/side 18 -   Duct aperture 22 -   Concrete aperture 24 -   Leg 26 -   Body/body side 28 -   Leg 32 -   Duct aperture 34 -   Concrete aperture 36 -   Body side 38 -   Leg 42 -   Duct aperture 44 -   Concrete aperture 46 -   Body 48 -   Leg 52 -   Leg 62 -   Duct chair 801 -   Form walls 802, 804 -   Open end 806 -   Rebar lattice 808 -   Duct support aperture 810 -   Duct 812 -   Alignment leg 814 -   Deck 906 -   Reinforcement 910 -   Duct 912 a, 912 b -   Support column 1002 -   Pre-stressed concrete beam 1004 -   Deck 1006 -   Pre-stress cable 1008 -   Design 1102 -   Set up form side 1104 -   Reinforce and embed 1106 -   Duct through duct chair 1108 -   Place duct and chair 1110 -   Reinforce and embed 1112 -   Set up form side 1114 -   Cast concrete into form 1116 -   Cure concrete 1118 -   Pre-stress 1120 -   Remove form 1122

DETAILED DESCRIPTION

FIG. 12 is a diagram of a PRIOR ART bar chair for holding rebar in place during concrete pouring operations. It may be seen to be completely unsuited by structure to holding ductwork in place. FIG. 13 is a diagram of a PRIOR ART bar chair of a different type. Both types and other common types are largely used to hold rebar in place during concrete pouring, and as such, merely need a flat surface or area of supports which will prevent rebar from drifting one direction when concrete is poured. However, these structures will not serve adequately in the context of trying to prevent motion at any location except close to the bottom surface of a pour, that is, the prior art may serve adequately when pouring a flat apron onto flat ground, as the rebar resting atop the device will be held up off the ground during the pour, however, in a tub beam, the form is oriented at an angle to the horizontal and a prior art chair would simply tumble down the inside of the form.

FIG. 9 is a greatly simplified cross sectional view of a prior art U-tub beam with an imposed load. Deck 906, the imposed load, is supported by the “tub” shaped beam below it. The beam may be seen to contain both reinforcement 910 and also ducts 912 a, 912 b, which contain pre-stressing cables. It will be understood that the pre-stressing of the structure by means of the cables contained in the ducts will provide a great deal of additional strength to the concrete U-tub beam, strength above that of non-pre-stressed concrete. Seen from the side, a bridge section made in this manner would look somewhat like FIG. 10. FIG. 10 is a partial cross-sectional side view of a simple bridge structure showing a single “pre-stressing strand” cable in use in a support beam. Support column 1002 supports one end of a pre-stressed concrete beam 1004, which in turn supports the imposed load of deck 1006. The scale of such structures may be quite large, for example, deck 1006 may be an eight lane highway, with columns 1002 more than 100 feet tall. Such a highway bridge may have long sections comprising a single U-tub beam 1004 (and as seen in cross-section in FIG. 9, already referenced). Pre-stressing cable 1008 may be seen in partial cross-section. The effectiveness of cable 1008 in providing extra strength to the bridge is dependent upon the proper positioning of the cable 1008: in the wrong location or orientation it may provide no strength to the concrete by failing to properly pre-stress the concrete. Worse, in some cases the cable 1008 may actually reduce the strength of the concrete if the mis-alignment brings the cable too close to the surface of the U-tub beam.

Thus, it would be preferable to provide a device able to ensure proper alignment of the pre-stressing cable in such a U-tub beam. In numerous other contexts, it would preferable to provide exact location of a wide variety of embedments in a concrete cast article.

The term concrete as used herein refers to any mixture of cement, water, aggregate whether fine or course, and additional admixtures such as are often used at the present time. The term “an aperture dimensioned and configured to allow semi-liquid concrete to pass therethrough” therefor may in turn refer to various sizes of aperture, as a larger aperture will be required for mixtures having relatively course aggregate, in a state of partial cure, having constituent admixtures which impact the viscosity of the concrete or are otherwise less prone to pass through an aperture than other mixes, while smaller apertures may be used in more typical circumstances.

It will be understood that the device of the present invention is substantially depicted in the context of a concrete tub beam or the like with simple concrete mixtures and a limited range of embedments and reinforcements, however, the invention is not so limited and may be used with a wide range of aggregates, admixtures, water-reducers, retarders, accelerators, air-entraining admixtures, corrosion inhibitors, mineral admixtures, prestressing, pretensioning, post-tensioning, a wide variety of strand sizes and duct sizes, a wide range of duct and strand spacings and arrangements, a wide variation in the quantities of ducts, strand anchors, strand couplers, epoxy coatings and other coatings, indented strands and various strand profiles, prestressing bars, and even with non-prestressed concrete structures and reinforcements. It may be used with a wide variety of deck systems and panels, diaphragm casting, water-cement ratios, heat application regimes, planned voids, and other aspects of concrete casting. It may be used with precast and cast-in-place construction.

FIG. 1 is a planform diagram of a first embodiment of the device having four conduit apertures and shorter alignment legs. The diagram may be either a top or bottom view of the device, which has a substantially planar (flat) two dimensional body with various apertures therethrough and alignment legs extending therefrom in one, two or three dimensions so as to provide an exact alignment to ducts passing through duct aperture 12. Duct aperture 12 will have a diameter which may be varied as required to match to a particular duct on a particular job.

Concrete access aperture 14 may similarly vary in dimension and shape in order to provide maximum concrete access in the form with minimum blockage of concrete during pouring. It will be understood that large webs on the body of the device are generally undesirable as they are likely to promote voids within the concrete, an obvious safety issue. Thus the webwork of the body 12 of the device may be interrupted by one or more concrete access apertures 14 so that as liquid concrete enters the form during pouring, the concrete penetrates efficiently, without voids occurring behind the invention.

Leg 16 may extend from the body on one, two, three, four or more sides, so as to maintain the device in proper alignment within the concrete form and thus maintain the duct, and thus the cable within the duct, in the proper alignment. Note that the ducts used are not necessarily limited to pre-stressing strand ducts, they may be ducts for other cables (electrical and so on) or for deliberate passages through the device or for another purpose or function desired.

Body/side 18 may advantageously be made of polymer/plastic, preferably a mixture having advantageous material properties when embedded in a concrete matrix. Metal may also be used, as may wood, advanced composite materials, combinations thereof and other suitable materials now known or later developed.

In the presently preferred embodiment and best mode presently contemplated for carrying out the invention, the dimensions of the device will be specified for the nature of the concrete structure being cast. That is, a device for use in a concrete shell 24 inches in thickness might advantageously have legs and body spanning a total width of 24 inches, so as to have the ends of the legs rest on both form sides during construction. A device for use with three ducts of 4.5 inches diameter may of course advantageously have three duct apertures of approximately 4.5 to 5 inches diameter, and so on.

FIG. 2 is a planform diagram of a second embodiment of the device having four conduit apertures and longer alignment legs. The diagram may be either a top or bottom view of the device. Duct aperture 22, concrete aperture 24 and body 28 may be substantially as previously described, however, it may be seen that leg 26 may be a different length than legs on other portions of body 28. By this means, the exact placement and orientation of the cable ducts may conveniently be provided anywhere within the concrete structure, not merely in the exact center of the shell.

In the presently preferred embodiment and best mode presently contemplated for carrying out the invention, four or more legs are found to provide the best support, alternative embodiments with less may be used as convenient, however, the use of four or more legs appears to provide the best alignment.

FIG. 3 is a planform diagram of a third embodiment of the device having three conduit apertures and shorter alignment legs. The diagram may be either a top or bottom view of the device. Leg 32, duct aperture 34, and concrete aperture 36 may be seen to occupy different relative positions in relation to each other. In comparison to the first two embodiments, there is not a pair of legs projecting from an area of the body located in between two duct apertures (in contrast to leg 16 of FIG. 2), the size of concrete access holes is different and so on.

Body side 38 may be seen to be either straight, curved, or a combination of both, and may include angles and other shapes useful in alignment, for example, projections designed to grasp other embedments.

FIG. 4 is a planform diagram of a fourth embodiment of the device having three conduit apertures and longer alignment legs on one side. The diagram may be either a top or bottom view of the device. Again, leg 42, duct aperture 44 and concrete aperture 46 may vary in their placement on body 48, with legs of differing length and only three ducts. Thus, it may be seen that the range of combinations of the elements of the invention is quite broad.

FIG. 5 is a side view of an alternative embodiment of the device having three alignment legs per side. Leg end 52 may be seen projecting therefrom, as in FIG. 6 (a side view of an alternative embodiment of the device having two alignment legs per side) leg/leg end 62 may be seen. The ends of the legs may rest against the opposing sides of the concrete form so as to provide the desired alignment. FIG. 7 is an end view of the device, showing that sides of the device may if desirable be plain, without legs projecting therefrom.

FIG. 8 is an extremely simplified cross sectional view of an embodiment of the device in use while a concrete section form, either open top or not, is being prepared.

Duct chair 801 sits between form walls 802, 804, at a position somewhat below form top 806. Rebar lattice 808 (some elements seen in cross section as circles, other elements seen longitudinally as long members) may be seen in place, as may duct support aperture 810, through which duct 812 passes.

Significantly, it may be seen that alignment leg 814 holds the device in place against one, or in the best mode, BOTH form walls 802, 804, providing proper alignment to the duct 812. In past methods, wiring of the duct into place was quite common, however, use of wire was extremely labor intensive and testing at one concrete casting company has shown that wiring may not effectively hold the ducts in proper placement during the concrete pour.

FIG. 11 is a flow chart of an exemplary embodiment of the method of the invention.

The first step of most concrete casting will be design, step 1102, of both the article and then the concrete form to make the article. After design, step 1104 is the setting up of a first side of the form, for example, the interior wall of the tub (reference numeral 804 in FIG. 8) or the exterior wall (reference numeral 802 in FIG. 8). Usually, the exterior wall would be the first wall, however, it is conceivable that it might be done in reverse order, or even that the walls might be made after all the embedments, though this is not the best mode contemplated.

Reinforcement and other embedments are then placed in the form at step 1106. Rebar mats are one obvious example of this.

In prior practice, the rebar mats might then be used as a support structure to wire in the ducts which would hold the pre-stress strand. However, as previously noted, testing has revealed that this may not be sufficiently reliable.

Duct may then be placed through duct chair at step 1108, and then the duct and chair may be secured into the form at step 1110. However, it is also possible to place the chairs into the form and run the ductwork therethrough and remain within the scope of the invention claimed herein.

Additional reinforcement and embedding may occur at step 1112.

Setting up of the other form side 1114 may not be necessary in a “one sided” form, however, in the best mode now contemplated, the method of the invention is used with “shell” type forms such as beams. Note that setting up the form's first side 1104 may occur as late in the process as concurrent with step 1114.

Casting of concrete into the form at step 1116 is the step in which prior art devices (wire) often failed to secure the duct work in place. This step is the point at which the concrete is finally introduced into the form, and it is during this step that the concrete access apertures (such as aperture 14 of FIG. 1) may allow concrete to pass freely through the device, preventing the formation of voids.

Curing of concrete (step 1118) may as previously noted occur with various heat regimes (electric heat, steam heat and others) or without, with or without curing agents and so on. Pre-stressing of the concrete using the pre-stressing cable 1120 may occur at this time or at a later time, even at the actual job site.

Removal of the form at step 1122 completes the process and allows transportation to the job site, unless the cast is occurring at the construction site. Removal may occur as early as concurrent with step 1116 or anytime thereafter.

It is important to understand that the order of steps shown in FIG. 11 is merely exemplary. For example, the interior form side may be constructed first and the exterior last, or the embedments and reinforcements may be placed first and both form sides later, the ducts may be placed and then the duct chairs added (using embodiments having split ring duct apertures), the duct chairs may be installed and then the duct run, stressing may occur at a first time interval after curing or even at the construction site and so on and so forth in numerous permutations and combinations.

All dimensions and configurations of the device may have a wide range of values. For example, for a first cast concrete item, the values of Table One might be used:

TABLE ONE Duct Aperture Diameter 3.375 inch Concrete Aperture Diameter 0.675 inch Leg Length  2.0 inch

END TABLE ONE

However, it will be understood that the dimensions of Table One, like the layouts shown in the diagrams, are merely exemplary. Each manufacturer of duct and cable makes differing sizes of duct, requiring different sizes of duct aperture. Each bridge section may be a unique width, requiring different leg lengths. And pouring conditions (how liquid the concrete is at the moment of pouring, the composition of aggregates and admixtures and so on) may drastically impact the size of the concrete aperture. Thus Table Two is an equally valid size of device, even though the dimensions may be seen to be radically different.

TABLE TWO First Duct Aperture Diameter: 1.125 inch Second Duct Aperture Diameter:   12 inch First Concrete Aperture Diameter: 0.125 inch Second Concrete Aperture Diameter:  2.75 inch First Leg Length:  0.5 inch Second Length:  12.5 inch

END TABLE TWO

From these dimensions it may be seen that a single chair might have two lengths of legs (for example if the ducts are to be maintained quite close to one side of a thick wall, an admittedly unusual situation but within the scope of the patent claims made herein). There may be multiple diameters and shapes of concrete access apertures, depending on the shape of web of the body, and there may be multiple duct diameters if different cables or purposes are being met by the ducts embedded in the concrete construction.

Thus, the device may vary quite a bit: duct apertures may be “split” so as to allow them to be placed around a duct rather than the duct fed through the aperture, apertures may be shapes other than circular, leg length may vary, the device may be offset from the center of the concrete shell and so on and so forth.

The disclosure is provided to allow practice of the invention by those skilled in the art without undue experimentation, including the best mode presently contemplated and the presently preferred embodiment. Nothing in this disclosure is to be taken to limit the scope of the invention, which is susceptible to numerous alterations, equivalents and substitutions without departing from the scope and spirit of the invention. The scope of the invention is to be understood from the appended claims. 

1. A concrete form duct chair of a concrete form having both a first cross sectional width and a first pre-stressing strand duct, the first pre-stressing strand duct having a first pre-stressing strand duct diameter, the concrete form duct chair comprising: a generally flat body; a first duct aperture passing through the body, the aperture having a first duct aperture diameter approximately equal to such first pre-stressing strand duct diameter; first and second alignment legs projecting from the body, the alignment legs and body dimensioned and configured to extend for a total width approximately equal to such cross sectional width of such concrete form; and a first concrete access aperture passing through the body, the concrete access aperture dimensioned and configured to allow semi-liquid concrete to pass therethrough.
 2. The concrete form duct chair of claim 1, wherein the material of duct chair comprises one member selected from the group consisting of: polymer, metal, wood, and composites thereof.
 3. The concrete form duct chair of claim 1, further comprising: third and fourth alignment legs projecting from the body, the third and fourth alignment legs and body dimensioned and configured to extend for a total width approximately equal to such cross sectional width of such concrete form.
 4. The concrete form duct chair of claim 1, further comprising: a second duct aperture passing through the body, the aperture having a second duct aperture diameter approximately equal to such first pre-stressing strand duct diameter.
 5. The concrete form duct chair of claim 1, further comprising: a second concrete access aperture passing through the body, the second concrete access aperture dimensioned and configured to allow semi-liquid concrete to pass therethrough.
 6. A method of casting concrete structures comprising the steps of: a) erecting a first concrete form side having an internal cross sectional width to make a concrete form; b) providing at least one duct chair having a generally flat body and a first duct aperture passing through the body, the aperture having a first duct aperture diameter approximately equal to such first pre-stressing strand duct diameter, the generally flat body further having at least first and second alignment legs projecting from the body, the alignment legs and body dimensioned and configured to extend for a total width approximately equal to such cross sectional width of such concrete form, the body further having a first concrete access aperture passing through the body, the concrete access aperture dimensioned and configured to allow semi-liquid concrete to pass therethrough; c) securing the at least one duct chair and a duct passing through the duct aperture into the concrete form; and d) casting concrete into the concrete form.
 7. The method of casting concrete structures of claim 6, further comprising: e) placing a first mat of reinforcing steel members into the concrete form prior to securing the duct chair and duct into the concrete form.
 8. The method of casting concrete structures of claim 6, further comprising: f) placing the duct through the duct chair aperture prior to securing the duct chair and duct into the concrete form.
 9. The method of casting concrete structures of claim 6, further comprising: g) placing the duct through the duct chair aperture after securing the duct chair into the concrete form.
 10. The method of casting concrete structures of claim 6, further comprising: h) securing the duct chair in place using fasteners.
 11. The method of casting concrete structures of claim 10, wherein the fasteners further comprise one member selected from the group consisting of: wires, flexible fasteners of plastic/polymer, string, twine, rope, cable, screws, nails, brads, tacks, bolts, snap fasteners, hook-and-loop fabric, sleeves, and combinations thereof.
 12. The method of casting concrete structures of claim 6, further comprising: i) placing a second mat of reinforcing steel members into the concrete form after securing the duct chair and duct into the concrete form.
 13. The method of casting concrete structures of claim 6, further comprising: j) erecting a second concrete form side defining the internal cross sectional width between the first and second concrete form sides.
 14. The method of casting concrete structures of claim 6, further comprising: k) providing a first layer of steel plating in the form.
 15. The method of casting concrete structures of claim 6, further comprising: l) allowing the concrete to cure after pouring.
 16. The method of casting concrete structures of claim 6, further comprising: m) stressing the concrete casting after pouring.
 17. The method of casting concrete structures of claim 16, further comprising: n) stressing the concrete casting immediately after pouring.
 18. The method of casting concrete structures of claim 16, further comprising: o) stressing the concrete casting at a first time duration after pouring.
 19. The method of casting concrete structures of claim 6, further comprising: p) separating the concrete casting from the form. 